reyna ricin, 16, from laporte, indiana. wendy felton, 16, from marion, indiana. michelle dewey, 20, in indianapolis, indiana. all of these cases went unsolved. officials believed only one man knew what happened. >> we knew he was responsible for several deaths. >> reporter: and to get answers it would take a risky, unusual plan. send a convicted drug dealer undercover into a dangerous prison to about friend an alleged serial killer. >> i'm not a serial killer hunter. i said so how am i going to do this? >> at stake, answers. >> wondering where she is, wondering what happened. >> peace for grieving family. >> you want to find her, bring her home and you can't. >> and one man's freedom. >> you don't just give outs candy and say you're free to go. i went through hell and back. >>> early each day donna wrightler greets her daughter trisha. >> i say hello to this picture every morning. i say good morning. every morning. i look at that and i can hear her say "hi, mom." >> trisha was very kindhearted. very smart. >> reporter: as a child, says father gary, trisha lit up